Hyatt Hotels says it found malicious software in about 250 of its properties that may have exposed customers' credit- and debit-card numbers and other information to hackers.

It's the first time the hotel operator has listed the hotels affected since it announced it found malware at its hotels in December.

The hotel chain does not know at this time how many customers were affected, a Hyatt spokeswoman said on Thursday.

Hyatt Hotels said the malware was present between July and December within payment-processing systems at its restaurants, spas, front desks and other areas in its hotels.

Cardholder names, card numbers and expiration dates may have been exposed, the company said.

Several other hotel chains reported being hacked last year, including Starwood, Trump Hotel Collection and Mandarin Oriental.

Hyatt said the malware was found at many of its brands, including the Park Hyatt, Hyatt Regency and Andaz. About 100 of the hotels affected were in the US. The rest were abroad in cities including London, Paris and Shanghai.